(Sub-)Plinian eruption at Anatahan volcano, Mariana Islands (Pacific Ocean) (copy 1)

This image was released by NASA Tuesday April 5, 2005; it shows a thick cloud of ash erupted from the Anatahan Volcano, Mariana Islands (Pacific Ocean). According to the Washington Volcanic Ash Advisory Center, a series of low-level eruptions starting on April 4 have created this plume.

A large explosive eruption occurred at Anatahan volcano, Mariana Islands (Pacific Ocean) at 0300 on April 6 (local time), 1700 April 5 UT. The eruption produced an ash plume that reached the highest altitude thus far during its current eruption - about 50,000 feet (ca. 16 km).

Seismic signals began to climb slowly at about 2200 local time (1200 UT) on April 5, and the Washington VAAC began seeing increased ash on satellite imagery at that time. The seismicity peaked about 0300 on April 6 (local time), 1700 April 5 UT. The upper level (50,000 ft) ash plume is blowing east to southeast and a lower level (15,000 ft) ash plume blowing toward the southwest; the plume extends more than 250 nautical miles (ca. 400 km).

The Emergency Management Office, Office of the Governor, CNMI, has placed Anatahan Island off limits until further notice and concludes that, although the volcano is not currently dangerous to most aircraft within the CNMI airspace, conditions may change rapidly, and aircraft should pass upwind of Anatahan or beyond 10 nautical miles downwind from the island and exercise due caution within 10 nautical miles of Anatahan.

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Background: The first historical eruption of Anatahan began 10 May 2003 after several hours of increasing seismicity. A phreatomagmatic eruption sent ash to over 30,000 feet and deposited about 10 million cubic meters of material over the island and sea. A small craggy dome extruded in late May and was destroyed during explosions on 13-14 June after which the eruption ceased.

The second historical eruption began about 9 April 2004 after a week or so of increasing seismicity. That eruption primarily comprised phreatomagmatic (steamy strombolian) explosions every minute or so and occasionally sent ash up to several thousand feet. That eruption ended on 26 July 2004.

The third historical eruption of Anatahan began on 6 January 2005 after three days of precursory seismicity. Frequent phreatomagmatic explosions began to occur, occasionally throwing one meter bombs a hundred meters in the air and sending ash 10,000 feet high and 60 km downwind. By 20 January explosions were occurring 3 to 10 seconds apart and fresh ejecta and small lava flows had filled the innermost crater to nearly the level of the pre-2003 East Crater floor.
The eruption peaked during 26 January 26 through 2 February, during which time ash rose as high as 15,000 to 20,000 feet and blew 150 km downwind, and vog nearly 600 miles downwind. The eruption apparently died out on 14 February, by which time the 2003 crater floor had essentially been entirely covered by fresh lava to a diameter of about one kilometer. The eruption restarted on 14 March for three days but never reached more than 10-20% of the intensity of the late-January phase of this eruption.
The eruption restarted again for five days on 21 March and again late on 28 March, both times with seismic amplitudes peaking at about half the maximum intensity of the late January phase of the 2005 eruption. During the last two weeks of March a small new cinder cone has formed and near the peak in activity on the 25th, ash briefly rose as high as about 19,000 feet altitude.

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SOURCE: adapted from USGS Anataha eruption update

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